Project Summary The intestinal villi that line the lumen of the small intestine is often susceptible to damage caused by immune-related disorders, infections, and medications. For example, in patients with celiac disease, consumption of gluten causes their body to mount an immune attack in the small intestine, leading to atrophy or blunting of the villi. In most cases, adhering to a strict gluten-free diet allows for the villi to recover completely. However, in over one-third of patients, the villi fail to recover and remain damaged, often referred to as persistent villous atrophy. Currently, it is not well understood why some patients can restore their villi and others cannot. Furthermore, the underlying mechanisms of villous repair after damage are poorly understood, and there are no medical therapies available to stimulate the process. In this proposal, we describe a novel injury-induced villous regeneration model using poly(I:C), a synthetic analog of dsRNA. Poly(I:C) provides not only a simple and reproducible means to injure the villi but also an opportunity to characterize the repair process that follows. Using this model to damage the mouse villi, we have discovered a previously unrecognized epithelial cell type, which we name villous injury-associated epithelial (VAE) cells that mediate the first phase of villous repair. Identified by their expression of claudin-4, VAE cells rapidly cover the surface of each collapsed villus to re-establish the epithelial barrier. This is soon followed by a second phase of repair characterized by the loss of VAE cells and regeneration of the villi. We believe that VAE cells that mediate the first phase of repair are crucial for the proper recovery of villi after damage. As this study is the first to report the existence of VAE cells, in Aim 1, we will further characterize these cells through the use of various lineage tracing strategies. With this approach, we will be able to address questions regarding the identity, plasticity, and fate of VAE cells. In Aim 2, we will determine the signals that drive the formation of VAE cells. Our preliminary data suggests that IL-17 may be a key stimulus. Together, the findings generated by these aims will expand our understanding of how intestinal villi recover after injury, with therapeutic implications for celiac disease and other conditions that damage the gut lining.